1. Field of the Invention
The present invention relates to a photothermographic material. In particular, the present invention relates to a photothermographic material for scanners, image setters and so forth, which is suitable for photomechanical process. More precisely, the present invention relates to a photothermographic material for photomechanical process that shows high sensitivity, high Dmax (maximum density) and low fog and can provide images suitable for use in photomechanical process.
2. Description of the Related Art
There are known many photosensitive materials having a photosensitive layer on a support, with which image formation is attained by light-exposing imagewise. Those materials include those utilizing a technique of forming images by heat treatment as systems that can contribute to the environmental protection and simplify image-forming means.
In recent years, reduction of amount of waste processing solutions is strongly desired in the field of photomechanical process from the standpoints of environmental protection and space saving. Therefore, development of techniques relating to photothermographic materials for use in photomechanical process is required, which materials enable efficient exposure by a laser scanner or laser image setter and formation of clear black images having high resolution and sharpness. Such photothermographic materials can provide users with simpler and non-polluting heat development processing systems that eliminate the use of solution-type processing chemicals.
Methods for forming images by heat development are described in, for example, U.S. Pat. Nos. 3,152,904 and 3,457,075 and D. Morgan and B. Shely, xe2x80x9cThermally Processed Silver Systems Axe2x80x9d, Imaging Processes and Materials, Neblette, 8th ed., compiled by J. Sturge, V. Walworth and A. Shepp, p.2 (1969). Such photothermographic materials comprise a reducible non-photosensitive silver salt (e.g., silver salt of an organic acid), a photocatalyst (e.g., silver halide) in a catalytically active amount and a reducing agent for silver, which are usually dispersed in an organic binder matrix. While the photosensitive materials are stable at an ordinary temperature, when they are heated to a high temperature (e.g., 80xc2x0 C. or higher) after light exposure, silver is produced through an oxidation-reduction reaction between the reducible silver salt (which functions as an oxidizing agent) and the reducing agent. The oxidation-reduction reaction is accelerated by catalytic action of a latent image generated upon exposure. The silver produced from the reaction of the reducible silver salt in the exposed areas shows black color and provides contrast with respect to the non-exposed areas, and thus images are formed.
European Patent Publication (hereinafter referred to as EP-A) 762,196, Japanese Patent Laid-open Publication (Kokai, hereinafter referred to as JP-A) 9-90550 and so forth disclose that high-contrast photographic property can be obtained by incorporating Group VII or VIII metal ions or metal complex ions of such a metal into photosensitive silver halide grains for use in photothermographic materials, or incorporating a hydrazine derivative into the photosensitive materials. Further, U.S. Pat. No. 5,545,515 discloses use of hindered phenols as a reducing agent and use of acrylonitrile compounds as a nucleating agent (ultrahigh contrast agent).
Furthermore, there are also already reported examples of use of phenol compounds as a reducing agent, which compounds have an amino group substituted with an electron-withdrawing group as a substituent (e.g., sulfonamidophenol compounds). For example, as described in JP-A-49-80386, JP-A-5-257227 and JP-A-10-221806, there are known methods of individually utilizing 2,6-dichloro-4-benzenesulfonamidophenol, p-benzenesulfonamidophenol and so forth as a reducing agent. However, even use of these compounds cannot improve sensitivity and cannot solve the problems concerning change of photographic performance (in particular, fog) during storage of photosensitive materials. Meanwhile, there is also known a method of using an aminophenol derivative together with a reducing agent as reported in JP-A-2000-267222. However, it does not satisfy the requirements of high Dmax (maximum density), low fog and high contrast. Accordingly, it has been desired to provide a photothermographic material for photomechanical process that shows high sensitivity, high Dmax (maximum density) and low fog and can provide images suitable for use in photomechanical process.
The objects of the present invention are to solve the aforementioned problems of the prior art. That is, a first object to be achieved by the present invention is to provide a photothermographic material that shows high sensitivity, high Dmax (maximum density) and low fog, and can provide images suitable for photomechanical process, in particular, as a photothermographic material for photomechanical process, more specifically, a photothermographic material for scanners, image setters and so forth. A second object to be achieved by the present invention is to provide a photothermographic material that can be prepared by coating of an aqueous system, which is advantageous for environment and cost.
The inventors of the present invention assiduously studied in order to achieve the aforementioned objects. As a result, they found that an excellent photothermographic material that provided the desired effects could be obtained by using a particular bisphenol compound and a particular phenol compound in combination in an image-forming layer, and thus accomplished the present invention.
That is, the present invention provides a photothermographic material comprising (a) a photosensitive silver halide, (b) a reducible silver salt, (c) a reducing agent represented by the following formula (1), (d) a binder and (e) a compound represented by the following formula (2) on the same surface of a support. 
In the formula (1), V1 to V8 each independently represent a hydrogen atom or a substituent, and L represents a bridging group consisting of xe2x80x94CH(V9)xe2x80x94 or xe2x80x94Sxe2x80x94 where V9 represents a hydrogen atom or a substituent. 
In the formula (2), X1 represents a substituent, and X2 to X4 each independently represent a hydrogen atom or a substituent, provided that X1 to X4 do not represent hydroxy group and X3 does not represent a sulfonamido group. The substituents represented by X1 to X4 may bond to each other to form a ring. R1 represents a hydrogen atom, an alkyl group, an aryl group, a heterocyclic group, an amino group or an alkoxy group.
Preferably, in the formula (2), R1 represents a hydrogen atom, an aryl group, a heterocyclic group, an amino group, an alkoxy group or an alkyl group having 1-7 carbon atoms. More preferably, in the formula (2), at least one of X1 and X3 is an electron-withdrawing group, and R1 is an aryl group or an alkyl group having 1-7 carbon atoms. Still more preferably, in the formula (2), both of X1 and X3 represent a halogen atom, and R1 represents an aryl group or an alkyl group having 1-7 carbon atoms. Most preferably, in the formula (2), both of X1 and X3 represent a chlorine atom or a bromine atom, X2 and X4 represent a hydrogen atom or an alkyl group, and R1 represents an aryl group.
Preferably, the photothermographic material of the present invention further contains a nucleating agent (ultrahigh contrast agent). Further, it is preferably has an undercoat layer containing gelatin between the support and the photosensitive layer.
The photothermographic material of the present invention provides high Dmax (maximum density), high contrast and low fog, in the presence of a nucleating agent and thus it has photographic properties suitable for use in photomechanical process. It also provides good photographic properties of high Dmax and low fog, even if it does not contain a nucleating agent.